Scanning apparatuses are widely used for scanning images of paper documents. The scanned contents of the paper documents can be converted into electronic files in order to be further stored, processed or spread. With increasing development of scanning technologies, the scanning apparatuses have experienced great growth and are now rapidly gaining in popularity. In the early stage, the scanning apparatus can scan one side of the document. For scanning both sides of the document, the document should be manually turned over after one side of the document has been scanned in order to sequentially scan the other side of the document. However, the process of manually turning over the document is troublesome. Recently, a duplex scanning apparatus has been developed to scan both sides of the document.
FIG. 1 is a schematic side view illustrating a conventional duplex printing apparatus. As shown in FIG. 1, the conventional duplex printing apparatus 1 comprises a sheet entrance 10, a sheet exit 11, a sheet feeding channel 12, a sheet transfer channel 13, an inverting channel 14, an image reading module 15, a transfer roller assembly 16, a first sheet sensing module 17, and a second sheet sensing module 18. The sheet feeding channel 12 is arranged between the sheet entrance 10 and the sheet transfer channel 13. The sheet transfer channel 13 is arranged between the sheet feeding channel 12 and the sheet exit 11. A first end of the inverting channel 14 is connected to the junction D11 between the sheet feeding channel 12 and the sheet transfer channel 13. A second end of the inverting channel 14 is connected to the sheet transfer channel 13. The image reading module 15 is located in the sheet transfer channel 13 for reading the image of a document. The transfer roller assembly 16 comprises a plurality of rollers 161-163 for transferring the document that is located within the sheet feeding channel 12, the sheet transfer channel 13 and the inverting channel 14.
The operations of the duplex printing apparatus 1 will be illustrated by referring to the sheet transfer paths S11˜S16 of FIG. 1. After the duplex printing apparatus 1 is activated, a document P11 is transmitted into the sheet feeding channel 12 through the sheet entrance 10. Then, the document P11 is transmitted from the sheet feeding channel 12 to the sheet transfer channel 13, so that the image of the first side P11A of the document P11 is read by the image reading module 15. After the reading operation is performed by the image reading module 15, the document P11 is transmitted to the junction D12 between the inverting channel 14 and sheet transfer channel 13. Then, the document P11 is transmitted to the inverting channel 14. Then, the document P11 is introduced into the sheet transfer channel 13 again, so that the image of the second side P11B of the document P11 is read by the image reading module 15. After the reading operation is performed by the image reading module 15, the document P11 is transmitted to the sheet exit 11.
The first sheet sensing module 17 is used for sensing the transmitting status of the document in the sheet feeding channel 12. When the document is transferred through the first sheet sensing module 17, the first sheet sensing module 17 generates a first sensing signal. The second sheet sensing module 18 is used for sensing the transmitting status of the document in the inverting channel 14. When the document is transferred through the second sheet sensing module 18, the second sheet sensing module 18 generates a second sensing signal.
FIG. 2 is a schematic perspective view illustrating the first sheet sensing module of the duplex printing apparatus of FIG. 1. The first sheet sensing module 17 comprises a first optical sensor 171 and a first sensing arm 172. The first optical sensor 171 has a first emitting part 1711 for emitting a light beam and a first receiving part 1712 for receiving the light beam. The first sensing arm 172 has a first rotating part 1721, a first contacting part 1722, and a first sheltering part 1723. The first contacting part 1722 and the first sheltering part 1723 are fixed on the first rotating part 1721.
The first rotating part 1721 has a cylindrical shape. In addition, both ends of the first rotating part 1721 are pivotally coupled with two portions of a supporting member 173, respectively. In a case that the first sensing arm 172 is not triggered, the first contacting part 1722 is partially exposed to the sheet feeding channel 12. Meanwhile, the first sheltering part 1723 is arranged between the first emitting part 1711 and the first receiving part 1712 to shelter the light beam. Consequently, the light beam from the first emitting part 1711 fails to be received by the first receiving part 1712. In a case that any document is transferred through the sheet feeding channel 12 to trigger the first contacting part 1722 of the first sensing arm 172, the first contacting part 1722 is toppled down by the front edge of the advancing document. At the same time, the first sensing arm 172 performs a rotating action with said first rotating part 1721 serving as an axle center, so that the first sheltering part 1723 is moved. Under this circumstance, the light beam from the first emitting part 1711 can be received by the first receiving part 1712, so that a first sensing signal is generated.
FIG. 3 is a schematic perspective view illustrating the second sheet sensing module of the duplex printing apparatus of FIG. 1. The second sheet sensing module 18 comprises a second optical sensor 181 and a second sensing arm 182. The second optical sensor 181 has a second emitting part 1811 for emitting a light beam and a second receiving part 1812 for receiving the light beam. The second sensing arm 182 has a second rotating part 1821, a second contacting part 1822, and a second sheltering part 1823. The second contacting part 1822 and the second sheltering part 1823 are fixed on the second rotating part 1821.
The second rotating part 1821 has a cylindrical shape. In addition, both ends of the second rotating part 1821 are pivotally coupled with two portions of a supporting member 183, respectively. In a case that the second sensing arm 182 is not triggered, the second contacting part 1822 is partially exposed to the inverting channel 14. Meanwhile, the second sheltering part 1823 is arranged between the second emitting part 1811 and the second receiving part 1812 to shelter the light beam. Consequently, the light beam from the second emitting part 1811 fails to be received by the second receiving part 1812. In a case that any document is transferred through the inverting channel 14 to trigger the second contacting part 1822 of the second sensing arm 182, the second contacting part 1822 is toppled down by the front edge of the advancing document. At the same time, the second sensing arm 182 performs a rotating action with said second rotating part 1821 serving as an axle center, so that the second sheltering part 1823 is moved. Under this circumstance, the light beam from the second emitting part 1811 can be received by the second receiving part 1812, so that a second sensing signal is generated.
The controlling mechanism of the duplex printing apparatus 1 will be illustrated as follows. In a case that the duplex printing apparatus 1 is operated in a single-side image scanning mode and the first sheet sensing module 17 generates the first sensing signal, a next document P12 will be transmitted into the sheet feeding channel 12 through the sheet entrance 10. In a case that the duplex printing apparatus 1 is operated in a double-side image scanning mode and the second sheet sensing module 18 generates the second sensing signal, the next document P12 will be transmitted into the sheet feeding channel 12 through the sheet entrance 10. In other words, regardless of the operating mode of the duplex printing apparatus 1, a plurality of documents can be sequentially fed into the sheet feeding channel 12. Moreover, any two adjacent ones of these documents are transferred through the sheet feeding channel 12, the sheet transfer channel 13 and the inverting channel 14 at the same spacing interval.
However, since the controlling mechanism of the duplex printing apparatus 1 needs two or more optical sensors 171 and 181, the conventional duplex printing apparatus 1 is not cost-effective. In other words, the conventional duplex printing apparatus should be further improved.